The present invention relates the art of yarn twisting, and more particularly, to the false twisting of yarns or strands as an integral component of a complete yarn process such as false twist texturing of thermoplastic yarns.
In the past, in this field, manufacturers of texturing equipment have devised a large number of different types of devices for imparting twist to a moving thermoplastic filament which is temporary in nature in that as the yarn passes the false twisting device, the twist disappears thus giving rise to the designation of the yarn as having been false twisted. With thermoplastic filaments, where the yarn is heated while in the twisted state and then cooled prior to untwisting, bulk and stretch characteristics are imparted to the yarn since the thermoplastic yarns tend to return to their twisted state when relaxed.
In attempting to increase the production capacity of false twisting machines, attention has been, to a large measure, directed to improvement of the false twisting device itself. These endeavors have resulted in the use of rotating tubes having pins therein about which the yarn is wrapped so that when the tube is rotated at high speeds, twist is imparted to the moving yarn strand. In other developments, friction discs have been employed where the yarn is pulled over the periphery of one or more discs which impart twist to the yarn by virtue of the frictional contact of the rotating discs with the moving yarn. See, in this regard, U.S. Pat. Nos. 3,232,037, 3,668,856 and 3,861,129, as well as the references cited in these patents for representative examples of prior false twisting devices.
One of the primary disadvantages of the devices of the prior art, such as those mentioned above, is the maintenance and power consumption required to operate the devices. Further, once the devices are set up for a particular yarn, it is often impractical to impart any variations to the twist level imposed on the yarn without undue complications or great loss in operating time.
Attempts have been made by workers in this field to simplify the false twisting device and it has been determined that a satisfactory twisting operation can be effected by wrapping a multi-filament yarn about a pin and then moving the yarn with suitable tension past the pin. The frictional engagement of the moving yarn with the pin surface induces twist buildup upstream of the pin. See, in this regard, the Olson U.S. Pat. No. 3,069,837.
In the Olson device, it is recommended that the pin or wire disclosed make an angle of between 30.degree. to about 60.degree. to the yarn path with the wire or pin being slanted in the direction of the yarn travel in order to obtain non-alternating twist in the yarn.
In the Wyatt U.S. Pat. No. 3,327,461, there is disclosed an apparatus for imparting twist to a moving yarn where the yarn is passed over either a freely or driven rotating frictional surface at particular helix angles.
The present invention provides an improvement in the pin type of false twisting devices and, in part, is based on the discovery that where the pin is set within a specific angular range relative to the yarn path, the amount of twist that can be imposed on the moving yarn is greatly increased without interfering with the throughput velocity of the yarn. Further, the present invention contemplates the substitution of a pin twisting device for each yarn in a false twisting machine and a mechanism for varying the angle of intersection between the false twisting pin and the individual yarn paths whereby variations in the amount of twist imposed on the individual yarn strands can be obtained to result in an interesting effect in a resulting fabric. One such means incorporates a vibrating device for continually or randomly vibrating the pin about an axis perpendicular to the longitudinal axis of the pin to correspondingly vary the amount of twist imposed on an individual yarn strand and to allow real twist to pass the pin during such transient operation. Conversely, the present invention provides an arrangement where a common pin means is set at a predetermined angle and a plurality of individual yarn strands are wrapped around the pin means at spaced intervals so that the angle of intersection between the individual yarn paths and the pin means is substantially the same which will result in substantially uniform imposition of twist on the individual yarns.
A particular application of the present invention, which is the subject of a separate, co-pending application, involves the utilization of the pin twisting means where variations in the amount of twist imposed on the yarn are employed and the yarn is then fed immediately to a fabric forming machine such as a knitting machine or a loom for incorporation into the fabric. A wide variety of interesting fabric effects can be achieved by varying the twist inserted either randomly or according to a set pattern and considerable production costs can be saved by immediately incorporating the thus twisted yarn into a fabric.